I’m not sure I’m really praising these, as in fact they are a nuisance. We have all encountered them – the pieces which seem innocuous and straightforward, yet which consume the lion’s share of rehearsal, possibly leaving others unprepared. How can they be identified and the problem avoided?
I once sang in a performance of Messiah on limited rehearsal time with a choir of people who’d sung the work before and an enthusiastically evangelical conductor. He liked the text of But thanks be to God (possibly because a well-known chorus sets the same text) and included it, only to find that practically none of the choir knew it. And with its fragmented vocal lines it turned out to be rather difficult to learn. (It is one of Messiah‘s less successful choruses adapted from a duet, and is almost always cut along with the preceding duet.)
Around the same time I sang at a wedding with a choir made up of guests which had one rehearsal immediately beforehand. We sang the hymns from a hymn book, but one hymn was played from a different hymn book and a very different arrangement. Unusually, there were no problems with the words, but sorting out the differences in the melody, working out where there were extra bars and so on, left little time for the polyphonic Mass setting we were also going to sing.
A more recent programme included a piece by Schütz which had never caused me much problem in the past but which took much longer than anything else to rehearse. The reason probably was that some in the choir weren’t used to singing German and there was a lot of text in this particular piece.
There are various morals to be drawn: do background research on whether a particular piece is well known; give the choir the exact same music as will be used by the accompanist; and check on linguistic competence! I’m sure there are many other ways that pieces can turn into cuckoos and deprive others of their rightful amount of rehearsal time.